| Summary: | 碩士 === 逢甲大學 === 環境工程與科學所 === 100 === Abstract
Constructed wetland (CW) could be used as waste water treatment facility which characterized in energy saving, low cost, and easy to maintain and operation. Similar studies have shown that under proper operation conditions, wetland can efficiently remove various pollutants. However, sewage water generally contains high BOD5, NH3-N and low DO and also results in eutrophication in the region of downstream.
The objective of this study is to evaluate the removal efficiency of pollutants by using wetland under two different conditions of pre-aeration. The study site of CW is located in Da-Ya, Taichung. This CW site was utilized to treat the community sewage water. The design of this CW is a combination of the traditional free waster system and subsurface flow system. In late experiment stage, additional soil absorption system was established in the end of the CW system in order to enhance the treatment efficiency.
Aeration equipments (artificial aeration, natural aeration) were utilized to elevate the DO of influent followed by water purification process while guiding to CW system. Operation parameters of CW system were hydraulic retention time (HRT)(7 days), Hydraulic loading rate(HLR) (0.057m3/m2/day),and batch inflow(3min/2hr). Study period was from Oct., 2010 to Aug., 2011, 309 days in total. CW system was conducted in two stages. The main purpose of the first stage was to compare the effect of pre-aeration conditions on water purification in CW system. On the second stage, it was to study the effect of the additional soil absorption system on water purification in CW system.
The results showed that the DO of influent increased after pre-aeration, but the function of artificial aeration was better than natural aeration. The mean removal efficiency of SS was 93% after two kinds of pre-aeration. The mean removal efficiency of BOD5 was up to 85%, whereas E-coli were totally removed. In comparison of the purification of nitrogen and phosphorus pollutants, the removal efficiency of TN and TP after artificial aeration was 39% and 32%, respectively. The removal efficiency of TN and TP after natural aeration was 25% and 27%, respectively. With the additional soil absorption system, the mean removal efficiency of SS was 95% after two kinds of pre-aeration. The mean removal efficiency of BOD5 was up to 90%. The removal efficiency of TN and TP was 83% and 79% using artificial aeration, compared to 62% and 66% using natural aeration.
It was concluded that pre-aeration process is important to increase the DO of influent. That means pre-aeration has positive effect on pollutant purification, especially for nitrogen pollutants removal. Our study provides evidence on significantly lowering the concentrations of various pollutants in effluent using our CW system. In addition, effluent from our CW system fulfills the water discharge criteria. More advantages of our CW system include small area required and efficient hydraulic retention time which is beneficial for future application.
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